There are several types of downhole cutting tools, such as drill bits, including roller cone bits, hammer bits, and drag bits, reamers and milling tools. Roller cone rock bits include a bit body adapted to be coupled to a rotatable drill string and include at least one “cone” that is rotatably mounted to a cantilevered shaft or journal. Each roller cone supports a plurality of cutting elements that cut and/or crush the wall or floor of the borehole and thus advance the bit. The cutting elements, either inserts or milled teeth, contact with the formation during drilling. Hammer bits generally include a one piece body having a crown. The crown includes inserts pressed therein for being cyclically “hammered” and rotated against the earth formation being drilled.
Drag bits, often referred to as fixed cutter drill bits, include bits that have cutting elements attached to the bit body, which may be a steel bit body or a matrix bit body formed from a matrix material such as tungsten carbide surrounded by a binder material. Drag bits may generally be defined as bits that have no moving parts. Drag bits having abrasive material, such as diamond, impregnated into the surface of the material which forms the bit body are commonly referred to as “impreg” bits. Drag bits having cutting elements made of an ultra hard cutting surface layer or “table” (generally made of polycrystalline diamond material or polycrystalline boron nitride material) deposited onto or otherwise bonded to a substrate are known in the art as polycrystalline diamond compact (“PDC”) bits.
An example of a drag bit having a plurality of cutting elements with ultra hard working surfaces is shown in FIG. 1. The drill bit 100 includes a bit body 110 having a threaded upper pin end 111 and a cutting end 115. The cutting end 115 generally includes a plurality of ribs or blades 120 arranged about the rotational axis (also referred to as the longitudinal or central axis) of the drill bit and extending radially outward from the bit body 110. Cutting elements, or cutters, 150 are embedded in the blades 120 at predetermined angular orientations and radial locations relative to a working surface and with a desired back rake angle and side rake angle against a formation to be drilled.
FIG. 2 shows an example of a cutting element 150, where the cutting element 150 has a cylindrical cemented carbide substrate 152 having an end face or upper surface (“substrate interface surface”) 154. An ultrahard material layer 156, also referred to as a cutting layer, has a top surface 157, also referred to as a working surface, a cutting edge 158 formed around the top surface, and a bottom surface, referred to as an ultrahard material layer interface surface 159. The ultrahard material layer 156 may be a polycrystalline diamond or polycrystalline cubic boron nitride layer. The ultrahard material layer interface surface 159 is bonded to the substrate interface surface 154 to form a planar interface between the substrate 152 and ultrahard material layer 156.